The present invention relates to a position detection apparatus for use with a mobile object, such as automobiles, airplanes or ships.
FIG. 1 of the accompanying drawings shows a conventional position detection apparatus. This position detection apparatus is mounted on a car when it is in use. A position detecting means 1 detects the position of a car and indicates a detected position of the car in the form of position information comprising latitude and longitude. A memory means 2 comprises a CD-ROM (compact disc-read-only memory) and a CD-ROM player for reproducing the CD-ROM. Map data of every place are stored in the CD-ROM. The memory means 2 is controlled by detected position information from the position detecting means 1 and position information entered by the operator so that a map is selected from the CD-ROM in accordance with latitude and longitude of that position information and a reduced scale selected by the operator. Selected map information is supplied to a display means 3. On the other hand, the detected position information from the position detecting means 1 also is supplied to the display means 3 and displayed on the map as a mark such as an arrow by the display means 3. AS the display means 3, there may be used a cathode-ray tube, a liquid-crystal display device, a plasma display device, etc.
A GPS receiver, which is an example of the position detecting means 1, will be described with reference to FIG. 2. Before describing the GPS receiver, a meaning and a measuring principle of the GPS will be described below in brief. Officially, GPS is referred to as xe2x80x9cNAVSTAR/GPSxe2x80x9d, and xe2x80x9cNAVSTAR/GPSxe2x80x9d is a combination of capital letters of NAVigation system with Time And Ranging/Global Positioning System. According to the measuring principle of the GPS, delay times of radio waves transmitted to the Earth from a plurality of GPS satellites orbiting the Earth are measured, and the position of a mobile object is measured by obtaining a present position of a mobile object on the Earth from the orbits of the GPS satellites. The position of the mobile object on the Earth can be obtained by measuring distances among the three GPS satellites and the present position of the mobile object on the Earth based on radio waves transmitted from the three GPS satellites. Furthermore, since a common error caused by errors of clocks of GPS receivers can be eliminated by measuring distances among four GPS satellites and the present position of the mobile object on the Earth, latitude, longitude and altitude of the position of the mobile object on the earth can be measured.
In FIG. 2, reference numeral 10 depicts an antenna for receiving radio waves from a GPS satellite (not shown). A microstrip antenna, for example, may be used as the antenna 10. A reception signal (spectrum diffusion signal) of 1.2 GHz or 1.5 GHz received at the antenna 10 is supplied through a coaxial cable (not shown) to a receiving unit 11, in which it is converted into an intermediate frequency signal with a low frequency. The intermediate frequency signal is supplied to a signal processing unit 12, in which it is spectrum-inverse-diffused to provide a message signal, a pseudo-distance signal and a code control signal. The signal processing unit 12 calculates a pseudo-distance by synchronizing the intermediate frequency signal based on the reception signal from the GPS satellite and a PRN (pseudo random noise) code generated therein. The message signal and the pseudo-distance signal are supplied to a microcomputer 13, in which they are computed for obtaining the present position of the mobile object. Therefore, there are obtained position data output (including data such as latitude, longitude, altitude, azimuth or speed).
The microcomputer 13 judges a GPS satellite which is able to receive radio waves at that time based on a clock signal from a clock circuit 14 belonging to the microcomputer 13 and almanac (calendar) data from the GPS satellite, and supplies the code control signal to the signal processing unit 12 based on a judged result thereby to generate the PRN code of the GPS satellite capable of receiving the radio wave. Then, position information from the output side, i.e, an output terminal 15 of the microcomputer 13 is supplied to the display means 3 (see FIG. 1) as described above.
When people are going to a destination by their own cars, they are communicating with each other through radio transmitter-receiver. Further, when a taxi control center issues commands to taxis with radio transmitter-receivers or taxis with radio transmitter-receivers communicate with each other, radio transmitter-receivers are used similarly.
If the position detection apparatus mentioned in the preamble is mounted on the car, then the present position of the car with the position detection apparatus mounted thereon can be detected clearly. However, only by the radio communication, it is impossible to accurately detect the positions of other cars and taxis.
In view of the aforesaid aspect, it is an object of the present invention to provide a position detection apparatus which can accurately detect user""own position and other user""s position.
According to an aspect of the present invention, there is provided a position detecting apparatus for a mobile object which is comprised of position detecting means mounted on a first mobile object for detecting a position of the first mobile object, transmitting-receiving means for transmitting position information of the first mobile object detected by the position detecting means and receiving position information of a second mobile object transmitted from the second mobile object, memory means for storing map information, and display means supplied with the position information of the first mobile object from the position detecting means, the position information of the second mobile object from the transmitting-receiving means and map information read out from the memory means in response to the position information of the first or second mobile object and displaying a map on which a mark indicative of the position of the first mobile object and/or the position of the second mobile object is put.
According to the present invention, user""s own position information from the position detecting means, other user""s position information from the. transmitting-receiving means and the map information from the memory means are supplied to the display means and thereby a map with marks indicating user""s own position or other user""s position or user""s and other user""s position put-thereon is displayed.